In semiconductor manufacturing, lithographic apparatus is used to apply patterns onto a substrate by selectively exposing a photoresist layer on the substrate to a radiation source. The size and/or density of features in the patterns may be limited by the wavelength of the radiation source used by the lithographic apparatus. Extreme ultraviolet (EUV) lithography, which uses extreme ultraviolet (EUV) radiation or soft x-ray, i.e. radiation with wavelength shorter than 130 nm, has become one of the lithography methods for forming smaller semiconductor devices.